Definition of A noun from the Oxford Advanced Learner's Dictionary

     

    A

     noun
    noun
    BrE BrE////
     
    ; NAmE NAmE////
     
    (also a)(pl. As, A’s, a’s
    BrE BrE//eɪz//
     
    ; NAmE NAmE//eɪz//
     
    )
     
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  1. 1 [countable, uncountable] the first letter of the English alphabet ‘Apple’ begins with (an) A/‘A’.
  2. 2 A [countable, uncountable] (music) the 6th note in the scale of C major
  3. 3[countable, uncountable] the highest mark/grade that a student can get for a piece of work or course of study She got (an) A in/for Biology. He had straight A's (= nothing but A's) all through high school.
  4. 4A [uncountable] used to represent the first of two or more possibilities Shall we go for plan A or plan B?
  5. 5A [uncountable] used to represent a person, for example in an imagined situation or to hide their identity Assume A knows B is guilty.
  6. see also A-frame, A level, A-road
    Idioms from one place to another For me a car is just a means of getting from A to B. including everything there is to know about something He knew his subject from A to Z.
See the Oxford Advanced American Dictionary entry: A